JP2007232518A - Natural circulation boiling water reactor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a channel structure of a lattice channel, which reduces flow induced vibration of a flow regime of a two-phase (gas-liquid) flow produced, when a plurality of vertical lattice channels are formed by partitions and the inner side of a chimney is used as an ascending channel of a coolant. <P>SOLUTION: A plurality of vertical lattice channels 11a-1, 11a-2 are formed by upper/lower lattice structure members 11-1, 11-2 within the circular tubular chimney 11 installed above a core 7 inside a pressure vessel 6. A branching/confluent zone 37 in which the lattice channels 11a-1, 11a-2 have different channel cross-sections is provided between partition end faces 28, 29 of the upper/lower lattice structure members 11-1, 11-2 to change the flow regime of the two-phase (gas-liquid) flow into a flow regime mixed or combined with a flow regime such as a churn flow when the two-phase (gas-liquid) flow ascends from the lattice flow channel 11a-1 to the lattice flow channel 11a-2 so that flow induced vibration load produced in the flow regime of the churn flow is reduced to secure the structural soundness of the chimney and economy is achieved in performance work for maintaining the soundness and making periodic inspection of the reactor. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a natural circulation boiling water nuclear reactor, and more particularly to a chimney flow path structure installed on a reactor core to obtain a natural circulation coolant circulation driving force due to a density difference of the coolant.

In a natural circulation boiling water reactor (hereinafter referred to as BWR), a reactor core is housed in a reactor pressure vessel, and a cylindrical reactor core shroud is provided so as to surround the reactor core. A cylindrical chimney is provided on the core so as to lead to this.
A coolant ascending channel is formed inside the core shroud and chimney, and a downcomer is formed outside as a coolant descending channel between the inner periphery of the reactor pressure vessel. As a result, in the reactor pressure vessel, the circulation channel for the natural circulation of the cooling water by the coolant circulation driving force based on the density difference is constituted by the downcomer, the core lower plenum, and the ascending channel.

In a BWR equipped with a circulation channel for the natural circulation of coolant in the reactor pressure vessel, the coolant heated by receiving heat from the core in the middle of the circulation is saturated with gas and liquid in a saturated state with steam. It becomes a phase flow, rises in the ascending flow path that exits the chimney from each fuel assembly in the core, and is separated into water and steam by the steam separator. Steam is supplied to a turbine or the like, and water is returned to the downcomer side. Further, the steam after working in the turbine is condensed and then returned to the reactor pressure vessel (downcomer side) through the feed water inlet nozzle.
The coolant returned to the downcomer is heated in the core and rises in the ascending flow path from the core to the chimney, and the density is lower than the coolant in the two-phase saturated state, which is based on the density difference. The downcomer is lowered by the coolant natural circulation driving force. The flow of the coolant descending the downcomer reverses upward in the lower plenum of the core, enters the core again from below and is heated and rises in the ascending flow path.

In such a BWR having a circulation channel in the reactor pressure vessel, the coolant in the reactor pressure vessel is naturally circulated instead of being forcedly circulated using a recirculation pump ( For example, see Patent Literature 1 and Patent Literature 2).
Therefore, the biggest difference between a natural circulation type BWR and a forced circulation type BWR that forcibly circulates the coolant with a recirculation pump is that the system and equipment for circulating the coolant are simplified. It is.

In addition, with the expectation of improvement in the circulation efficiency of the coolant by natural circulation, in the transverse cross section of the cylindrical chimney, the axial height increases from the outside toward the center along the radial direction, for example, A chimney having an upright staggered grid flow path structure divided into an outermost peripheral region, an outer region, an inner region, and the like is provided on the core so as to be raised through a gas-liquid two-phase flow from the core. A natural circulation type BWR is also known (see, for example, Patent Document 3).
Japanese Patent Laid-Open No. 06-265665 (see paragraph number 0019 and FIG. 1) Japanese Unexamined Patent Publication No. 08-094793 (see paragraph numbers 0022 to 0023 and FIG. 1) Japanese Patent Publication No. 07-027051 (see claim 1, lines 7 to 21 in the right column on page 4 of the specification, and FIG. 1)

The inventors of the present application performed a flow test of a two-phase flow of a vertical upward flow using an air-water two-phase flow experimental apparatus simulating a chimney lattice channel. During the flow test, the flow rates of the two-phase air and water were varied.
As a result, it was found that a flow induced vibration (FIV) load was applied to the flow path partition walls forming the lattice flow paths.

For example, as shown in FIG. 9, the central portion in the cross section of the lattice channel 40 is occupied by a gas phase (air bubbles), and the liquid flows along the inner wall surface 40 a of the lattice channel 40 outside the bubbles. A state 41 in which a phase (water) is present and a state 42 in which the inside of the channel cross-section is substantially filled with a liquid phase are alternately repeated to form a two-phase flow mode close to a so-called Churn flow. It was found that pressure fluctuations of several kPa to several tens of kPa were applied to the partition walls.
Moreover, in this experiment, it turned out that the phase to the pressure fluctuation to the lattice partition between adjacent lattice flow paths differs.
This is because, in the churn flow in the lattice flow path, the void ratio distribution is not uniform in the height direction in the flow as described above, and the void ratio distribution in the height direction is the same between the lattice flow paths. This is considered to be due to the fact that it is not in phase and that the volume of the gas phase is different for each lattice channel.
Such a hydrodynamic vibration load may be adversely affected in the long term when a flow path partition that separates grid flow paths is formed by joining plate materials by welding or the like. There is sex.

  The present invention has been improved so as to effectively reduce the coolant vibration vibration load generated when the inside of the chimney is divided into a plurality of upright lattice channels to be used as the coolant ascending channel. An object of the present invention is to provide a natural circulation boiling water reactor equipped with chimneys having a flow channel structure.

  In order to solve the above problems, the natural circulation boiling water reactor according to the present invention includes a plurality of upright grid flows partitioned in a grid form inside a chimney installed on a core in a reactor pressure vessel. The present invention is characterized in that a channel is provided, and the cross section of the lattice channel has different regions in the height direction (Claim 1). And the said grid flow path is comprised in the height direction by the upper and lower grid structures (Claim 2), It is characterized by the above-mentioned. Furthermore, a gap is provided between the divided end faces of the upper and lower lattice structures (claim 3).

  According to the natural circulation boiling water nuclear reactor of the present invention, when the coolant heated in the core becomes a gas-liquid two-phase flow in a saturated state and rises and passes through each lattice channel of Chimney, The flow mode such as churn flow, which is a factor causing hydrodynamic vibration load in the channel, is mixed by, for example, branching or merging in the region of the grid channel where the channel cross section is different in the height direction, and the flow is converted. The Thereby, generation | occurrence | production of the pressure fluctuation resulting from the churn flow caused in the process in which the gas-liquid two-phase flow ascends the lattice channel is suppressed, and the hydrodynamic vibration load associated therewith can be reduced. That is, according to the present invention, a flow mode in which water and steam flow separated, such as a churn flow, is converted into a flow in which water and steam are dispersed.

  Moreover, the lattice flow path which has the cross-sectional area of the flow path of a different area | region in a height direction can be easily implement | achieved by the stacking | stacking combination of the divided | segmented upper and lower lattice structures. Further, the lattice flow paths of the upper and lower lattice structures are communicated with each other through a gap provided between the divided end faces of both lattice structures. As a result, pressure fluctuations in which the phase generated in the height direction of each lattice flow path differs depending on the flow mode of the churn flow interferes with each other through the gap, so that the pressure fluctuations in adjacent lattice flow paths are made uniform. It is possible to reduce the hydrodynamic vibration load more effectively.

The present invention can effectively reduce the hydrodynamic vibration load generated in each lattice channel when the inside of the chimney is divided into a plurality of upright lattice channels and the inside of the chimney is used as the coolant ascending channel.
Further, the branching and mixing of the coolant in the height direction of the lattice channel also has the effect of making the chimney void ratio distribution uniform.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.
FIG. 1 is a longitudinal sectional view showing an outline of a natural circulation boiling water reactor of the present invention provided with a chimney according to a first embodiment.

≪Outline of nuclear reactor≫
As shown in FIG. 1, a natural circulation boiling water reactor (hereinafter referred to as “reactor”) 1 includes voids generated in a reactor core 7 housed in a reactor pressure vessel (hereinafter referred to as “pressure vessel”). That is, the density difference (specific gravity difference) between the low-density coolant mixed with the vapor (gas phase) and the liquid coolant at the saturation temperature and the liquid coolant mixed with the feed water supplied from the feed water pipe 16b. Thus, a coolant circulation driving force necessary for natural circulation is obtained.

≪Reactor configuration≫
As shown in FIG. 1, a nuclear reactor 1 is provided with a cylindrical core shroud (hereinafter referred to as a shroud) 8 concentrically inside a pressure vessel 6 that is vertically long and has a cylindrical shape. The shroud 8 is supported by a shroud leg 8 a fixed to a shroud support 32 provided near the bottom of the inner surface of the pressure vessel 6. An annular space is formed between the outer peripheral surface of the shroud 8 and the inner peripheral surface of the pressure vessel 6, and this annular space is used as a downcomer 9 as a coolant downflow path.
Further, inside the shroud 8, the core 7 on which a large number of fuel assemblies 21 are mounted is supported and accommodated by the core support plate 22 and the upper lattice plate 23. A cylindrical chimney 11 is provided concentrically on the upper lattice plate 23 of the reactor core 7, and a coolant ascending flow path is formed inside the shroud 8 and the chimney 11.

  Above the downcomer 9, a water supply (not shown) that distributes the coolant supplied from the water supply inlet nozzle 17 into the pressure vessel 6 after being heated by the water supply heater 5 from the condenser 3 via the water supply pump 4. A sparger is provided in an annular shape. The coolant descending the downcomer 9 is introduced into the lower plenum 10 from the flow path between the shroud legs 8a.

The upper end of the chimney 11 is closed by a shroud head 12a. The shroud head 12a is provided with a predetermined number of coolant passage holes (not shown), and the steam-water separation for separating the steam-saturated water and the saturated water from the gas-liquid two-phase flow through the stand pipe 12b. Connected to vessel 12.
A steam dryer 13 is provided on the top of the steam / water separator 12 so that moisture contained in the saturated steam exiting the steam / water separator 12 is separated and removed.

  Further, on the chimney 11 closed by the shroud head 12a, the saturated cooling rising from the lower lattice channel 11a-1 described later of the chimney 11 through the upper lattice channel 11a-2. A shroud upper plenum (hereinafter referred to as an upper plenum) 11c is formed so that the materials meet (see FIG. 1).

A lower core plenum (hereinafter referred to as a lower plenum) 10 swelled downward in a substantially hemispherical shape is integrally formed at the lower part of the core 7. A core support plate 22 is provided between the lower plenum 10 and the core 7 as a boundary that separates the core 7 and the lower plenum 10, and an upper lattice plate 23 is provided above the core support plate 22. 21 and the control rod 24 are arranged in the horizontal direction.
The core support plate 22 is provided with circular through holes (not shown) at predetermined intervals. A control rod guide tube 25 is inserted into the through holes, and the lower portion of the control rod guide tube 25 penetrates the bottom of the pressure vessel 6. The control rod drive mechanism housing (hereinafter referred to as a CRD housing) 26a for accommodating the control rod drive mechanism 26 for moving the control rod 24 in the vertical direction is combined with the upper portion.
The fuel assembly 21 is placed on a fuel support fitting (not shown) attached to the upper end of the control rod guide tube 25, and the load is applied to the bottom of the pressure vessel 6 via the control rod guide tube 25 and the CRD housing 26a. I am trying to communicate.

  The fuel support fitting has a coolant inlet on a side surface, and an orifice (not shown) is provided therein to regulate the coolant flow rate. An opening is provided in the side surface of the control rod guide tube 25 corresponding to the coolant inlet of the fuel support bracket so that the coolant guided to the lower plenum 10 is guided into the fuel assembly 21 through the fuel support bracket. It has become.

The individual fuel assemblies 21 are surrounded by a rectangular tube channel box (not shown) to form individual flow paths in the axial direction. The channel box reaches the upper surface of the upper lattice plate 23. On the outside of the channel box of the rectangular tube, there is formed a flow path having a gap between the adjacent fuel assembly 21 and the flow rate of a predetermined ratio of coolant.
The control rod 24 has an effective portion containing a neutron absorbing material (not shown), and the effective portion is inserted between the four fuel assemblies 21 with the outer surface of the channel box as a guide.
On the other hand, a container lid 27 swelled upward in a substantially hemispherical shape is attached to the upper opening of the pressure vessel 6 so as to be detachable (openable / closable) by a number of stud bolts not shown. A steam dome 14 is provided inside the container lid 27.

  Note that the shroud head 12a, the stand pipe 12b, and the steam / water separator 12 are integrally assembled, and can be removed from the upper end of the chimney 11 at the time of periodic inspection of the nuclear reactor 1 or replacement of fuel. ing.

In this way, in the natural circulation reactor 1 having a structure in which the reactor cores 7 and chimneys 11 and the like schematically described are sequentially provided in the pressure vessel 6, as shown in FIG. The operation is performed in a state in which the material (light water) is put to a water level L at a height in the middle of the steam separator 12.
Then, the coolant supplied from the feed water inlet nozzle 17 is mixed with the saturated water separated by the steam separator 12, and the coolant indicated by the arrow A in FIG. The coolant flow descending the downcomer flows from the shroud leg 8a provided on the lower side of the shroud 8 to the lower plenum 10, reverses upward at the lower plenum 10, and flows again into the core 7 from below. Heated by the core 7.

By the heating from the core 7, the coolant A becomes a gas-liquid two-phase flow in a saturated state indicated by an arrow B in FIG. This gas-liquid two-phase flow rises from the lower lattice flow path 11a-1 of the chimney 11 through the upper lattice flow path 11a-2 through the gap 30 described later, and passes through the upper plenum 11c and the stand pipe 12b. Then, the steam-water separator 12 separates the saturated vapor in the gas phase indicated by the arrow C and the saturated water in the liquid phase indicated by the arrow D. In this way, the core 7 and the chimney 11 constitute a coolant ascending flow path inside.
The saturated steam C passes through the steam dryer 13 and is led from the steam outlet nozzle 15 to the turbine 2 by the main steam pipe 16a to be used for power generation.

On the other hand, the saturated water D is mixed with the coolant in the pressure vessel 6 and further mixed with the coolant supplied from the feed water inlet nozzle 17, and descends the downcomer 9 again from the shroud leg 8 a to the lower plenum 10. The lower plenum 10 is turned upside down, and again flows into the core 7 from below to be heated.
That is, the coolant returned to the downcomer 9 is mixed with the feed water, and is heated by the core 7 and rises more than the gas-liquid two-phase flow coolant that rises in the ascending flow path connected to the core 7 and chimney 11. Since the density is high at low temperatures, a cooling water natural circulation driving force based on the density difference (specific gravity difference) is generated, and the downcomer 9 is lowered.

<< Configuration of Chimney of First Embodiment >>
Next, the channel structure of the chimney lattice channel according to the first embodiment will be described with reference to FIGS. 2, 3, and 4. Here, description will be made with reference to FIG.
2 is a cross-sectional view taken along the line II-II in FIG. 1, FIG. 3 is a perspective view showing the upper and lower lattice structures of the chimney according to the first embodiment, and FIG. 4 is an upper and lower lattice structure. It is a cross-sectional view which expands a part and shows the combination arrangement relation of a lattice channel when a body is piled up, and the arrangement relationship between a lattice channel and a control rod cell of a core.

As shown in FIGS. 2 and 4, the chimney 11 includes upper and lower lattice structures 11-1 and 11-each having a plurality of lattice channels 11 a-1 and 11 a-2 partitioned in a lattice shape when viewed from above. 2 is provided inside.
The chimney 11 includes a cylindrical chimney cylinder 11d that surrounds the upper and lower lattice structures 11-1 and 11-2 (see FIG. 2). The chimney cylinder 11d is installed concentrically in, for example, the pressure vessel 6 and accommodates the upper and lower lattice structures 11-1 and 11-2 stacked in a concentric manner. Between the upper end and the shroud head 12a, it is formed at such a height that an upper space serving as the upper plenum 11c is secured (see FIG. 1).

≪Lattice structure construction≫
The upper and lower lattice structures 11-1 and 11-2 are divided into two in the height direction of the chimney 11, and are accommodated by being stacked and combined concentrically inside the chimney cylinder 11d. When the upper and lower lattice structures 11-1 and 11-2 are concentrically accommodated inside the chimney cylinder 1d, the upper and lower lattice structures 11-1 and 11-2 are accommodated so as to secure a gap 30 between the divided end faces 28 and 29 (see FIG. 1).
In addition, the clearance gap 30 does not collect saturated vapor | steam containing gas from the outer side to the center side in a cross section. In other words, it is preferable that the drift does not occur. In short, it is sufficient that the lattice flow paths 11a-1 and 11a-2 of the upper and lower lattice structures 11-1 and 11-2 communicate with each other and can be expected to have a uniform pressure effect.
As shown in FIGS. 3 and 4, the upper and lower lattice structures 11-1 and 11-2 include lattice flow paths 11 a-1 and 11 a-2 partitioned in a lattice shape by flow path partition walls 11 b. Has been. Incidentally, the flow path partition 11b is joined by welding or the like.

≪Lattice flow path configuration≫
Each lattice channel 11a-1 of the lower lattice structure 11-1 and each lattice channel 11a-2 of the upper lattice structure 11-2 are basically the same except for the arrangement with respect to the center of the core plane. Next, each lattice channel 11a-1 of the lower lattice structure 11-1 will be described. In addition, the arrangement | positioning of each grating | lattice flow path 11a-2 of the upper grating | lattice structure 11-2 is mentioned later.
Each lattice channel 11a-1 has a square channel cross section, and the size of the channel cross section (opening) is formed according to the array angle of the 2 × 2 array of control rod cells 31 on the core plane. (See FIG. 4). Therefore, the arrangement of each lattice channel 11a-1 is mirror-symmetric with respect to the 1/8 symmetry axis 35 with respect to the plane of the core, as shown in FIG. Incidentally, the control rod cell 31 has a control rod 24 arranged in the center of a 2 × 2 array of fuel assemblies 21.
That is, as shown in FIG. 2, normally, an angle of 45 ° is formed with respect to the respective symmetry axes of the X axis 33 and the Y axis 34 passing through the center P in the plane of the core 7 and the X axis 33 or the Y axis 34. And has a 1/8 symmetry axis 35 passing through the center P.

On the other hand, the arrangement of the lattice channels 11a-2 of the upper lattice structure 11-2 is as shown in FIG. 4 in each of the lattice channels 11a-1 of the 2 × 2 array of the lower lattice structure 11-1. The four corners of one lattice channel 11a-2 are positioned at the center of the cross section. Therefore, when a combination of the lower lattice structure 11-1 and the upper lattice structure 11-2 stacked from above is viewed from above, the four lattice channels 11a- are located at the center of each lattice channel 11a-2. Thus, the cross intersection P1 of the channel partition wall 11b forming 1 appears to be located.
In addition, it is suitable to form the lower end of the flow path partition 11b which partitions each grid flow path 11a-2 of the upper grid structure 11-2 into a knife edge shape or a streamline shape. Thereby, the pressure loss of the gas-liquid two-phase flow in the chimney 11 can be reduced.

As described above, one lattice channel 11a-2 of the upper lattice structure 11-2 is ¼ of the lattice channel 11a-1 of the 2 × 2 array of the lower lattice structure 11-1 below the upper one. The gas-liquid two-phase flow that rises in one lattice flow path 11a-1 of the lower lattice structure 11-1 becomes 4 by the flow partition 11b of the upper lattice structure 11-2. It will be branched into one flow. Then, a gas-liquid two-phase flow corresponding to ¼ area of the 2 × 2 array of lattice channels 11a-1 of the lower lattice structure 11-1 is converted into one lattice channel 11a of the upper lattice structure 11-2. -2 will join.
Thereby, the upper and lower lattice structures 11-1 and 11-2 between the respective lattice flow paths 11a-1 of the lower lattice structure 11-1 and the respective lattice flow paths 11a-2 of the upper lattice structure 11-2. A gas-liquid two-phase flow exits the split end face 28 and passes through the split end face 29 via the gap 30 between the split end faces 28 and 29 of the upper grid structure 11-2. By flowing in the path 11a-2, the flow path structure having the branch / merging region 37 in which the cross section of the flow path where branching and merging are performed is different in the height direction of the upper and lower lattice structures 11-1 and 11-2. Formed (see FIG. 5).

And, in the inspection such as the periodic inspection, the lattice channels 11 a-1 connected to the upper and lower lattice structures 11-1 and 11-2 in the height direction while the chimney 11 is installed inside the pressure vessel 6. Replacement work such as lifting and loading the fuel assembly 21 or the control rod 24 through 11a-2 can be performed (see FIG. 4).
That is, at the time of inspection such as periodic inspection, the fuel assembly 21 is pulled up and loaded through the lattice channels 11a-1 and 11a-2 of the chimney 11 while the chimney 11 is installed in the furnace pressure vessel 6. From the viewpoint of exchanging operations such as the above, the flow path partition walls 11b of the lattice flow paths 11a-1 and 11a-2 of the chimney 11 are square lattices opened in the upper grid plate 23 of the core 7 in units of control rod cells 31. It is preferable to configure so as not to block the hole (not shown).

Next, the flow of the gas-liquid two-phase flow rising up the lattice flow channels 11a-1 and 11a-2 having a flow channel structure having a branching / merging region 37 having a gap 30 and a flow channel cross-section different from each other with reference to FIG. explain. Here, description will be made with reference to FIG. 1 as appropriate.
FIG. 5 is a conceptual diagram provided for explaining the flow of the gas-liquid two-phase flow of the flow channel structure in the chimney lattice flow channel according to the first embodiment.
As shown in FIG. 5, the gas-liquid two-phase flow mixed with the vapor rising in each lattice channel 11 a-1 of the lower lattice structure 11-1 crosses the channel before it develops to the flow pattern of the churn flow. It reaches the branching / merging region 37 with each lattice channel 11a-2 of the upper lattice structure 11-2 having a different surface. At this time, as the gas-liquid two-phase flow rises, vapor bubbles collect at the center of the cross section of the lattice channel 11a-1.

The vapor bubbles in the lattice channel 11a-1 reached by the branching / merging region 37 are divided into, for example, four by the channel partition wall 1b of the lattice channel 11a-2, and cross the channel of the lattice channel 11a-2. It flows so as to be released near the four corners of the surface. Then, the vapor bubbles subdivided at the entrance of the lattice channel 11a-2 move to the central portion of the cross section of the lattice channel 11a-2 as it moves up the lattice channel 11a-2, Gas-liquid separation begins again to form large vapor bubbles.
That is, the gas-liquid two-phase flow that has risen through each lattice channel 11 a-1 of the lower lattice structure 11-1 passes through the branch / merging region 37 and each lattice channel 11 a of the upper lattice structure 11-2. -2 is branched into the gas flow and mixed with the gas-liquid two-phase flow that flows into the lattice flow channels 11a-2 from the other adjacent lattice flow channels 11a-1. At this time, the phases relating to the presence of liquid and gas (instantaneous void ratio) in each of the lattice channels 11a-1 and 11a-2 are random and do not match.

In this way, the lattice channel 1a-1 having the branch / merging region 37 that is divided into the upper and lower lattice structures 11-1 and 11-2 in the vertical direction and that has different channel cross-sectional areas in the height direction. 1a-2, the flow path structure in the height direction can suppress the development of the churn flow and suppress the pressure fluctuation caused by the churn flow.
Further, adjacent lattice channels 11 a-1 of the lower lattice structure 11-1 and adjacent lattice channels 11 a-2 of the upper lattice structure 11-2 flow through the gaps 30 in the branching / merging region 37. By doing so, pressure fluctuations interfere with each other between the flows exiting each grid flow path 11a-1 of the lower grid structure 11-1, thereby suppressing pressure fluctuations (fluid vibration). Become.

<< Configuration of Chimney of Second Embodiment >>
Next, the flow channel structure of the chimney lattice flow according to the second embodiment will be described with reference to FIGS.
FIG. 6 is a longitudinal sectional view showing an outline of the natural circulation boiling water reactor of the present invention provided with the chimney according to the second embodiment, and FIG. 7 is a top and bottom view of the chimney according to the second embodiment. 8 is a perspective view showing the lattice structure of FIG. 8, and FIG. 8 is a partial view of the combined arrangement of the lattice channels and the arrangement relationship between the lattice channels and the control rod cells of the core when the upper and lower lattice structures are overlapped. It is a cross-sectional view which expands and shows.
Note that the channel structure of the chimney 11 according to the second embodiment is the size and arrangement of each grid channel 11a-3 of the upper grid structure 11-2 as shown in FIGS. There is only a difference in form, and in other configurations, the same components are basically the same as the components of the chimney 11 according to the first embodiment described above, and the same components are denoted by the same reference numerals, and redundant description is omitted. To do.

That is, each lattice channel 11a-3 of the upper lattice structure 11-2 of the chimney 11 according to the second embodiment has a square channel cross section, and the size of the channel cross section (opening) is the same. The lower grid structure 11-1 is formed in accordance with the array angle of the 2 × 2 array of lattice channels 11a-1 in the cross section. Then, as shown in FIG. 8, each grid channel 11a-3 is arranged at the center of each cross section of one grid channel 11a-3 of the upper grid structure 11-2. -1 of the 3 × 3 array of lattice channels 11a-1, the central lattice channel 11a-1 is located concentrically, and the crossing of the single lattice channel 11a-1 Each side and four corners of the cross section of each lattice channel 11a-1 adjacent to each other at each side and four corners of the surface are positioned. Therefore, when the combination of the lower lattice structure 11-1 and the upper lattice structure 11-2 stacked from above is viewed from above, one lattice flow is formed in the cross section of each lattice passage 11a-3. A part of each of the eight lattice flow paths 11a-1 in total adjacent to the path 11a-1 appears to be located.
In addition, it is suitable to form the lower end of the flow path partition 11b which partitions each grid flow path 11a-2 of the upper grid structure 11-2 into a knife edge shape or a streamline shape. Thereby, the pressure loss of the gas-liquid two-phase flow in the chimney 11 can be reduced.

  Thus, the upper and lower lattice structures 11-1 and 11-3 between the lattice flow paths 11a-1 of the lower lattice structure 11-1 and the lattice flow paths 11a-3 of the upper lattice structure 11-3. Between the divided end faces 28 and 29, a branching / merging region 37 having a different flow path cross section flowing in the height direction through the gap 30 is formed. That is, as shown in FIG. 8, a total of nine grid channels 11a-1 adjacent to each other at each side and four corners of the cross section centering on one grid channel 11a-1 of the lower grid structure 11-1. The gas-liquid two-phase flow rising up is branched into eight flows by the flow path partition 1b of the upper lattice structure 11-2. In the 3 × 3 arrangement of the lower lattice structure 11-1, the gas-liquid two-phase flow corresponding to approximately 1/8 area of the single lattice channel 11a-1 and the lattice channel 11a-1 is converted into the upper lattice. In one structure flow path 11a-2 of the structure 11-2, it merges.

Therefore, according to the nuclear reactor 1 including the chimney 11 according to the second embodiment, it is possible to suppress the pressure fluctuation caused by the churn flow by suppressing the development of the churn flow as in the first embodiment. it can. Further, the adjacent lattice channels 11 a-1 of the lower lattice structure 11-1 and the adjacent lattice channels 11 a-3 of the upper lattice structure 11-2 communicate with each other through a gap 30 in the branch / merging region 37. By doing so, pressure fluctuations interfere with each other between the flows exiting each grid flow path 11a-1 of the lower grid structure 11-1, thereby suppressing pressure fluctuations (fluid vibration). Become.
And, in the inspection such as the periodic inspection, the lattice channels 11 a-1 connected to the upper and lower lattice structures 11-1 and 11-2 in the height direction while the chimney 11 is installed inside the pressure vessel 6. Replacement work such as lifting and loading the fuel assembly 21 or the control rod 24 through 11a-3 can be performed.

According to the nuclear reactor 1 provided with the chimney 11 of each embodiment configured as described above, the coolant heated in the core 7 becomes a gas-liquid two-phase flow in a saturated state, and the lower lattice structure 11-1. The gas-liquid two-phase flow is an element that causes fluid vibration when passing through each grid channel 11a-1 and each grid channel 11a-2 or 11a-3 of the upper grid structure 11-2. The development of flow patterns such as Churn flow is suppressed.
And the gas-liquid two-phase flow which raises each lattice flow path 11a-1 of the lower lattice structure 11-1 without developing to the flow pattern of a churn flow is the upper and lower lattice structures 11-1 and 11-2. The flow cross-sectional area formed between the divided end faces 28 and 29 is branched by different branch / merging regions 37 and mixed by being merged to convert the flow.
In other words, the liquid film flow along the inner wall surface of each lattice channel 11a-1 of the lower lattice structure 11-1 becomes a droplet state above, and each lattice channel 11a- of the upper lattice structure 11-2. 2 or distributed along the flow path partition wall 1b side of each of the lattice flow paths 11a-3 and flows so as to adhere to the inner wall surface of the flow path partition wall 1b and form a liquid film liquid. In addition, the vapor bubbles at the center in the channel cross section of each grid channel 11a-1 of the lower grid structure 11-1 are converted into each grid channel 11a-2 or each grid flow of the upper grid structure 11-2. It is subdivided by the flow path partition wall 11b that divides the path 11a-3, is divided into small-volume vapor bubbles, and flows into each lattice flow path 11a-2 or each lattice flow path 11a-3. Thereby, generation | occurrence | production of the pressure fluctuation resulting from the churn flow caused in the process in which a gas-liquid two-phase flow rises can be suppressed, and the hydrodynamic vibration load can be reduced.

  Further, the branching / merging region 37 can be easily realized by a stacked combination of the upper and lower lattice structures 11-1 and 11-2. That is, the upper and lower lattice structures 11-1 and 11-2 or the upper lattice structure with respect to the arrangement of the respective lattice channels 11a-1 of the lower lattice structure 11-1 in the cross section of each lattice channel 11a-3. This can be realized by changing the arrangement of the lattice channels 11a-2 of 11-2 or the lattice channels 11a-3.

  Further, the lattice channels 11a-1, 11a-2 or the lattice channels 11a-3 of the upper and lower lattice structures 11-1, 11-2 communicate with each other through a gap 30 provided between the divided end surfaces 28, 29. By doing so, pressure fluctuations with different phases generated in each of the lattice channels 11a-1, 11a-2 or each of the lattice channels 11a-3 interfere with each other through the gap 30. As a result, it is possible to equalize pressure fluctuations having different phases in each of the adjacent lattice channels 11a-1, 11a-2 or each of the lattice channels 11a-3, so that the hydrodynamic vibration load can be made even more effective. It can be expected to be reduced.

  Further, a plurality of lattice channels 11 a-1, 11 a-2 or each lattice channel 11 a-3 standing upright in the height direction of the chimney 11 are divided into upper and lower lattice structures 11-divided in the height direction of the chimney 11. 1 and 11-2, for example, the lattice structures 11-1 and 11-2 are transported to the construction site of the nuclear reactor 1, and the lattice structures 11-1 and 11-2 are transferred. It is possible to expect improvement in workability such as suspending and storing the inside of the pressure vessel 6 or pulling it up from the pressure vessel 6 at the time of periodic inspection.

Therefore, according to each embodiment, the hydrodynamic vibration load applied to the flow path partition walls 11b of the lattice flow paths 11a-1 and 11a-2 can be effectively reduced, and the chimney 11 during the reactor operation period can be effectively reduced. Or pressure fluctuations with different phases in the lattice flow paths 11a-1, 11a-2 or the lattice flow paths 11a-3 cause one lattice flow path 11a-2 or lattice flow path 11a- in the upper lattice structure 11-2. 3, the possibility of merging damage can be reduced. As a result, it can withstand long-term use, saves the trouble of inspection and maintenance at the time of periodic inspection of the reactor, and in the unlikely event, the chimney 11, the lattice channels 11a-1, 11a-2, or the lattice channel 11a The number of exchanges of the upper and lower lattice structures 11-1 and 11-2 having -3 can be reduced. Moreover, the economic loss due to the plant stop at the time of replacement can be minimized.
Further, a grid structure may be provided inside the chimney 11 that is divided into a plurality of upright grid channels 11 a-1, 11 a-2 or a grid channel 11 a-3 so that the inside of the chimney 11 is the coolant ascending channel. In the inspection such as the periodic inspection, the lattice channels 11a-1 and 11a connected in the height direction of the upper and lower lattice structures 11-1 and 11-2 while the chimney 11 is installed inside the pressure vessel 6. -2 or the lattice channel 11a-3, the fuel assembly 21 or the control rod 24 can be lifted and loaded. That is, there is no problem such as an increase in the number of processes during fuel replacement.

The specific configuration of the embodiment of the present invention is not limited to each of the above-described embodiments, and there are design changes and the like without departing from the gist of the present invention described in claims 1 to 3. However, it is included in the present invention.
For example, the division of the upper and lower lattice structures of the chimney having a plurality of upright lattice channels is not limited to the combination of the lower and upper lattice structures in two upper and lower stages, but three upper and lower stages (see FIG. 5). Can be divided into several stages such as four stages. That is, it can be arbitrarily set according to the height of the chimney.

Moreover, the division | segmentation height of a lower lattice structure and an upper lattice structure does not need to be the same. For example, the lower lattice structure side can be formed higher than the upper lattice structure side.
Further, when divided into several stages, the height of the lattice structure can be lowered step by step from the first stage placed on the core to the height direction. That is, it is possible to design in such a manner that the areas where the cross sections of the lattice flow paths are different from each other in the height direction from the core are increased step by step.
This is because the gas-liquid two-phase flow in a saturated state mixed with gas-liquid tends to develop as it rises vertically upward, so that the grid crosses the flow path from the core to the height direction. By gradually increasing the areas with different surfaces, mixing or interference due to the branching or confluence of gas-liquid two-phase flow will be repeated, suppressing the generation of churn flow (suppressing pressure fluctuation) and hydrodynamic vibration It can be expected to reduce the load even more effectively. However, it is necessary to provide an excessive area (separation / merging area, etc.) with different channel cross-sections in the height direction of the grid channel because it may cause an increase in pressure loss when the coolant is naturally circulated. It is desirable to keep it to a minimum.

  In addition, the grid channel arrangement structure may be such that the size of the channel cross section of the grid channel gradually increases from the center in the cross section of the upper and lower grid structures to the outside in the radial direction. it can. That is, the grid cross section of the grid channel group in the outer region is larger than the channel cross section of the grid channel group in the inner region of the central part of the grid structure, and the grid channel group of the outer region The cross section of the array of grid channels from the center to the outside in the radial direction, such as forming a larger cross section of the grid channels in the outermost peripheral region than the cross section of Can be changed.

  Further, the cross section of the lattice channel is not limited to a square, and can be formed in a polygon such as a rectangle, a triangle, and a hexagon. However, it is necessary to consider that it is possible to perform an exchange operation such as pulling up and loading the fuel assembly or control rod through the grid channel connected in the height direction.

  The present invention is applied to a natural circulation boiling water nuclear reactor, and hydrodynamic vibration (pressure fluctuation) caused by a gas-liquid two-phase churn flow in an ascending flow channel inside a chimney installed on the core ) Effectively.

1 is a longitudinal sectional view showing an outline of a natural circulation boiling water reactor of the present invention provided with a chimney according to a first embodiment. FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1 with the reactor pressure vessel omitted. It is a perspective view which shows the upper and lower lattice structures which have the chimney lattice channel which concerns on 1st Embodiment. It is a cross-sectional view which expands and shows a part of the state which stacked and combined the upper and lower lattice structures of the chimney according to the first embodiment. It is the conceptual diagram provided in order to demonstrate the flow of the gas-liquid two-phase flow in the lattice flow path of the chimney which concerns on 1st Embodiment. It is a longitudinal cross-sectional view which shows the outline of the natural circulation type boiling water reactor of this invention provided with the chimney which concerns on 2nd Embodiment. It is a perspective view which shows the upper and lower lattice structure which has a chimney lattice channel which concerns on 2nd Embodiment. It is a cross-sectional view which expands and shows a part of the state where the upper and lower lattice structures of the chimney according to the second embodiment are stacked and combined. FIG. 3 is a conceptual diagram of a grid channel used in an experimental apparatus that simulates a grid channel in order to investigate the flow mode of a churn flow of gas-liquid two-phase flow in the chimney grid channel.

Explanation of symbols

1 Natural Circulation Boiling Water Reactor 2 Turbine 6 Reactor Pressure Vessel 7 Core 8 Core Shroud 9 Down Comb (Down Channel)
10 Core Lower Plenum 11 Chimney 11-1 Lower Lattice Structure 11-2 Upper Lattice Structure 11a-1, 11a-2 or 11a-3 Lattice Channel (Upward Channel)
11b Channel partition 11c Upper plenum 11d Chimney cylinder 21 Fuel assembly 28, 29 Split end face 30 Gap 31 Control rod cell 37 Branch / merging area (area with different channel cross-section)

Claims (3)

A natural circulation boiling water nuclear reactor having a coolant circulation channel having an ascending channel inside and a descending channel outside by chimney installed on the core in the reactor pressure vessel. ,
The chimney is provided with a plurality of upright grid channels partitioned in a grid pattern, and the cross section of the grid channels has different regions in the height direction. Boiling water reactor.   2. The natural circulation boiling water reactor according to claim 1, wherein the lattice flow path is configured in a height direction by divided upper and lower lattice structures.   The natural circulation boiling water reactor according to claim 2, wherein a gap is provided between the divided end faces of the upper and lower lattice structures.

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